This invention relates to a novel coated workpiece having a machine-readable marking recessed therein, and to a novel method for making said workpiece.
U.S. patent application Ser. No. 041,091 filed May 21, 1979 by W. R. Miller describes an improved method for assembling parts for a cathode-ray tube including providing at least one tube part, such as the glass faceplate, which has a unique machine-readable coded marking, such as a bar-code marking, on an external surface thereof. This marking is read one or more times by machine during the manufacturing of the tube. Each time it is read, a control signal is generated in response to the reading, and then the signal is used to initiate a local process for action with respect to the tube part. The local process may be one or more of selecting and assembling another part to the workpiece, a series of processing steps applied to the workpiece, a recording of a historical record, etc. The marking must be made reliably at low cost, must be readable reliably at low cost and must survive the hostile environments of subsequent processing.
U.S. patent application Ser. No. 041,092 filed May 21, 1979 by P. M. Heyman discloses an improved workpiece which carries a machine-readable coded marking, such as a bar-code marking abraded into the surface of the workpiece. Also disclosed is a novel method whereby the abraded marking can be made on demand at relatively low cost and at relatively high rates of speed. Since the marking is abraded into the workpiece, it has substantially the same resistance to hostile environments as the workpiece itself. The abraded portions of the marking and the nonabraded portions therebetween have substantially different reflectances so that they can be read with commercial bar-code readers at low cost. The difference in reflectances is the difference in the reflectance of abraded areas, which are relatively more light scattering, and nonabraded areas, which are relatively less light scattering. It is desirable to provide a still higher difference in reflectances for each marking and a difference which is not dependent solely on the light-scattering qualities of the abraded and nonabraded portions of the marking.